It has been shown in the literature that a single mmWave BS equipped with a large number of antenna elements and operating over a very large bandwidth can also achieve highly accurate positioning performance [1]}. However, to accomplish this, the BS needs to rely on both temporal and angular channel parameters, e.g., time or time difference of arrival as well as Angles of Arrival (AoAs) or angles of departure. In principle, high-accuracy recovery of the angular channel parameters requires large-sized antenna arrays, and that of the temporal parameters requires large communications signal bandwidths. It is noted that, up to date, radio localization based on cellular network infrastructure is deemed as an additional functionality of BSs, implying that the network resources allocated to three-Dimensional (3D) localization (especially bandwidth/spectrum and time) should be minimized so that the major network functionality, which is wireless communications, will not be significantly affected [2]}. To this end, localization schemes that solely rely on angular channel parameters are highly desirable, since wideband operation is not necessary.
In this regard, in the recent work [3]}, multiple spatially distributed RISs, each equipped with a single Receive (RX) Radio Frequency (RF) and being capable to collect baseband measurements of spatially sampled versions of their impinging signal, were deployed to perform highly accurate 3D localization. However, the proposed framework necessitated wired/wireless backhaul links to gather the received signals from each RIS to a central processing unit, which was assigned with the localization computation task. This approach inevitably increases the deployment cost and the system's implementation complexity.
